Embodiments of the present invention relate to communication scenarios with a master device and a potential number of slave devices, where collisions by simultaneous communications of devices may occur.
In communication systems where a permanent synchronization between communicating devices is not maintained, collisions can occur. These collisions refer to the event, where multiple communication entities communicate simultaneously in a manner that communication resources are over utilized. In some scenarios, such collisions may even lead to a communication breakdown of a communication system.
A conventional system wherein collisions may occur is the so-called single wire protocol (SWP=Single Wire Protocol). One characteristic of SWP is a full duplex physical communication link, wherein data may be transferred in the voltage domain, in the following also referred to as S1, and in the current domain, in the following also referred to as S2, simultaneously. In other words, communication can be carried out by communicating on a single wire, utilizing voltage and current signals at the same time. For example, a first device could transmit data over the wire by using voltage signals to a second device, which in turn communicates data to the first device by adjusting a current, which is drawn from the first device.
SWP can for example be used to connect contactless front ends (CLF=Contactless Front End) to a subscriber identity module (SIM=Subscriber Identity Module) in mobile devices equipped with a contact less subsystem, which is also known as an NFC system (NFC=Near Field Communication). These systems may for example be implemented in mobile phones, mobile computers, etc. In some scenarios, communication between a CLF and a SIM may only be a point-to-point communication or interface. In other scenarios, there can be a potential need for a multi-point communication link, i.e. one SWP master may communicate to multiple SWP slaves. These scenarios can occur if multiple SWP slaves are present. In some scenarios, SWP slaves may be replaceable or removable secured elements.
In scenarios where multiple slave entities are present, collisions may occur in terms of simultaneous communication of said slave entities. Especially in a SWP scenario, collisions may occur, as SWP slaves can communicate using the S2 domain, i.e., by drawing a current from the master entity. In cases when multiple slaves draw current simultaneously from a master, the master may become overloaded. This can especially be relevant in scenarios where for communication stability, a current drawn by a slave is set to a higher value. In such scenarios, a current drawn by multiple slaves may exceed the limit of a master's output driver and may cause overloads, in particular possibly having undesirable side effects on, for example, the contactless subsystem which may only be powered from an RF-field (RF=Radio Frequency).